The present invention relates to a conical cheese and a method of forming the wound package of a conical cheese with a yarn guide device.
Yarn manufactured on rotor spinning machines differs from ring-spun yarn in its winding buildup behavior and in its unwinding behavior. Rotor yarn is less hairy than ring-spun yarn and can, therefore, be more easily unwound (easier release). However, the rotor yarn has a greater tendency to roll than ring-spun yarn, causing the wound yarn in the edge area of the cheese to be pressed to the outside by the yarn layers above it. As a result, a cheese can be formed that exceeds the normal winding traverse of, e.g., 150 mm and can grow to a width of 170 to 180 mm. Consequently, the end surfaces that are desired are no longer produced. Such phenomena occur with yarns made of natural fibers such as cotton, and especially with coarse yarns. Coarser yarns produce a more marked distortion of the end surfaces.
Problems can also occur on the end surfaces of wound packages in the preliminary stage of yarn manufacture in the case of wound fiber slubbings or roving yarns. U.S. Pat. No. 954,344 discloses that bulges will occur in winding construction on the end surfaces if slubbings or roving yarns are not twisted or are only slightly twisted. This problem occurs even though the displacement angle is more than 32°, which is customary in the prior art. This problem is exacerbated by the soft and loose structure of the fiber strands. Bulges can have a significant adverse effect on the further processing of the packages. According to U.S. Pat. No. 954,344, the bulges can be prevented by increasing the displacement angle, which otherwise remains the same, in the edge area of the package.
If cheese winding is performed at high yarn speeds in the cross winding, it can occur with average and coarse yarns, because of the inertia of mass, for the yarn to move past the bobbin edge at the deflection points of the traverse movement and to create a so-called skipped yarn defect. This defect leads to yarn breaks and hinders the further processing of the yarn.
The probability of the occurrence of such defects is significantly influenced by crossing angle α. Therefore, in the manufacture of cheeses the selection of the particular yarn crossing angle is of great significance. When a cheese is produced by “random winding,” the yarn crossing angle remains constant over the entire winding travel. On the other hand, when a cheese is produced using “precision winding,” the yarn crossing angle decreases with the increasing cheese diameter. The advantages of precision winding are, among other things, the fact that a cheese produced using precision winding has more running length, given the same bobbin volume, than a cheese produced using random winding. However, the crossing angle, which decreases with increasing cheese diameter, limits the permissible maximum diameter when manufacturing precision bobbins of staple fiber yarns since the winding cannot be carried out with small crossing angles with staple fiber yarns in order to avoid the defects occurring on the edges. For this reason, crossing angles of less than 28° should be avoided during rotor spinning, as described, e.g., in German Patent Publication DE 100 15 933 A1. Consequently, precision winding, especially when winding staple fiber yarns, can be used only under very limited conditions.
In a third winding type referred to as “stepwise precision winding,” the goal is a crossing angle that remains approximately the same over the winding travel. Even with stepwise precision winding, the above-described density problems and problems with the stability of the bobbin edge are only somewhat reduced in practice, but are not eliminated.
Generic German Patent Publication DE-AS 26 32 014 shows a conical cheese driven by circumferential friction from a roller. The drive roller has a narrow friction zone, having an elevated coefficient of friction, extending somewhat out of its middle surface. Ideally, the drive should take place only in the predetermined area of the friction zone of the cheese. However, the winding cheese can make contact, as the bobbin diameter increases, with the parts of the roller-shaped drive device that are located to the left and to the right of the predetermined friction zone. Consequently, the bobbin is no longer driven only in the friction zone, but is also driven at other locations on the circumference of the cheese. Since the length of the bobbin circumference viewed over the bobbin axis is different with conical bobbins, the speed of the cheese can fluctuate and become uncontrollable. In order to avoid this, the yarn crossing angle of the cheese represented in German Patent Publication DE-AS 26 32 014 and in parallel U.S. Pat. No. 4,266,734 is designed to be reduced in a limited range opposite the narrow friction zone of the drive roller in comparison to the yarn crossing angle outside of this friction zone. Consequently, the wound package's resistance to pressure is slightly increased in the predetermined, limited area. In addition, the friction zone of the drive roller and the area with a reduced yarn crossing angle of the conical cheese remain narrow.
New machine techniques, especially in the weaving mill, such as, e.g., air-jet weaving machines, place increased demands on the unwinding properties of the yarn. The requirements cannot be met, or are only insufficiently met, with the known winding constructions.